Influence of a plasma jet on different types of tungsten

The influence of a plasma producing nonstationary thermal loads akin to edge-localized modes in a tokamak on different types of tungsten is investigated. Tungsten is irradiated by a jet of a hydrogen plasma generated in a plasma gun. The plasma density and velocity are on the order of 10$^{22}$ m$^{-3}$ and 100–200 km/s, respectively, and the irradiation time is 10 $\mu$s. Two plasma flux densities, 0.70 and 0.25 MJ/m$^2$, are used. Structural modifications in irradiated single-crystal and hot-rolled tungsten samples, as well as in V$\underbar{\ }$MP and ITER$\underbar{\ }$D$\underbar{\ }$2EDZJ4 tungsten powders, are examined. It is found that the plasma generates a regular crack network with a period of about 1 mm on the surface of the single-crystal, hot-rolled, and V$\underbar{\ }$MP powder samples, while the surface of the ITER$\underbar{\ }$D$\underbar{\ }$2EDZJ4 powder is more cracking-resistant. The depth of the molten layer equals 1–3 $\mu$m, and the extension of intense thermal action is 15–20 $\mu$m. The material acquires a distinct regular structure with a typical grain size of less than 1 $\mu$m. X-ray diffraction analysis shows that irradiation changes the crystal lattice parameters because of the melting and crystallization of the surface layer. The examination of the V$\underbar{\ }$MP tungsten powder after cyclic irradiation by a plasma with different energy densities shows that high-energy-density irradiation causes the most significant surface damage, whereas low-energy-density irradiation generates defects that are small in size even if the number of cycles is large.